1. Field of the Invention
The present invention relates to a displacement detector which detects the variation of magnetic field by utilizing the variation of the resistance of a magnetoresistive element (hereinafter referred to as an MRE) and detects the motional condition of a moving body or a rotating body based on the detected magnetic field variation.
2. Related Arts
A conventional displacement detector using an MRE, the resistance of which varies according to magnetic variation, has been used in a wide variety of fields for the features thereof, such as reliable operation, high precision, high durability and easy downsizing.
As one such displacement detector, Watanabe et al., U.S. Pat. No. 5,359,287, discloses a sensor which comprises two pairs of MREs and detects the magnetic variation responsive to the revolution or displacement of the rotating body as a detection subject having gear teeth arranged at a constant pitch to detect the amount of the revolution or displacement of the detection subject. As illustrated in FIGS. 11 and 12, each of the MREs 14a, 14b, 14c and 14d installed in the sensor is so constructed by long strip portions and short strip portions alternately joined end to end for a plurality of times that the long strip portions are inclined by approximately 45.degree. or 135.degree. with respect to the direction B of magnetic force lines emitted from a bias magnet.
As there has been a strong demand for high-precision detection in recent years, it has become necessary to narrow the gear tooth pitch of the detection subject to increase the number of pulses per revolution of the rotating body.
If the gear tooth pitch is narrowed, in a case of the MRE arrangement shown in FIG. 11, as the magnetic force lines passing through the respective MREs 14a(14b) and 14c(14d) become different, there is a problem that high-accuracy detection is impossible. On the other hand, in a case of the MRE arrangement shown in FIG. 12, as the distances between the gear teeth and the respective MREs 14a through 14d differ from each other, there is also a problem that the resultant output is small.
To solve these problems, an MRE arrangement of two-layered structure in which the respective pairs of MREs 14a and 14c and MREs 14b and 14d disposed at angles of approximately 45.degree. and approximately 135.degree., respectively, to the direction B of magnetic force line are stacked as shown in FIG. 13 as proposed in Watanabe et al. Furthermore, a detector in which an even number of and at least four MREs 14e through 141 are disposed in parallel to each other and connected in series to each other as illustrated in FIG. 14 and proposed in the Japanese Unexamined Patent Publication No. 5-180664.
However, these devices have posed problems. In the detector illustrated in FIG. 13, as the structure is complicated, the manufacturing process is also so complicated that the detector becomes expensive. In the detector illustrated in FIG. 14, as more MREs are required compared with the detector illustrated in FIG. 13, and differential amplification circuits 12 are required for one half the number of the MREs 14e through 141, detector itself inevitably becomes not only larger in size but higher in cost.